WO-A-95/26499 discloses a holographic sensor, based on a volume hologram. The sensor comprises a holographic element, the element comprising an analyte-sensitive holographic support medium having an optical transducing structure disposed throughout its volume. Because of this physical arrangement of the transducer, the optical signal generated by the sensor is very sensitive to volume changes or structural rearrangements taking place in the analyte-sensitive matrix as a result of interaction or reaction with the analyte. For example, a sensor comprising a gelatin-based holographic medium may be used to detect trypsin. Trypsin acts on the gelatin medium, irreversibly destroying the integrity of the holographic support medium.
WO-A-031087899 describes a method for the continuous detection of an analyte in a fluid involving the use of a holographic sensor. The support medium of the sensor comprises a group which is capable of reacting reversibly with the analyte. Thus, when fluid is passed over the holographic element, any analyte present can be detected continuously.
In particular, WO-A-031087899 describes how a holographic sensor formed by the polymerisation of monomers including vinylphenylboronic acid may be used to detect glucose. The pendant phenylboronic acid groups can react reversibly with a cis-diol group of glucose, resulting in swelling of the holographic support medium. A limitation of this technology is that the sensor is only effective over a limited pH range; there remains the need for sensors which can detect glucose continuously over a range of conditions, in particular physiological conditions.